The same sort of parenthesised form is used for a macro invocation,
but in that case the arguments are not evaluated. See the
descriptions of macros for more on this (see Macros, and
see Syntax Rules).

constant

Number, string, character and boolean constants evaluate “to
themselves”, so can appear as literals.

123 ⇒ 123
99.9 ⇒ 99.9
"hello" ⇒ "hello"
#\z ⇒ #\z
#t ⇒ #t

Note that an application must not attempt to modify literal strings,
since they may be in read-only memory.

(quote data)

'data

Quoting is used to obtain a literal symbol (instead of a variable
reference), a literal list (instead of a function call), or a literal
vector. ' is simply a shorthand for a quote form.
For example,

Note that an application must not attempt to modify literal lists or
vectors obtained from a quote form, since they may be in
read-only memory.

(quasiquote data)

`data

Backquote quasi-quotation is like quote, but selected
sub-expressions are evaluated. This is a convenient way to construct
a list or vector structure most of which is constant, but at certain
points should have expressions substituted.

The same effect can always be had with suitable list,
cons or vector calls, but quasi-quoting is often easier.

(unquote expr)

,expr

Within the quasiquote data, unquote or , indicates
an expression to be evaluated and inserted. The comma syntax ,
is simply a shorthand for an unquote form. For example,

Within the quasiquote data, unquote-splicing or
,@ indicates an expression to be evaluated and the elements of
the returned list inserted. expr must evaluate to a list. The
“comma-at” syntax ,@ is simply a shorthand for an
unquote-splicing form.